1. Field of the Invention
This invention relates to information processing systems which utilize error correcting codes and which can benefit from the use of certain control signals. More particularly, the invention relates to incorporating special flag and/or status indicating code signals at random positions in serially ordered data without utilizing bit combinations which might otherwise normally be used to represent valid data.
2. Prior Art
There can be many situations in which it becomes desirable to include "flags" in fields of data that are utilized by an information processing system. These fields may be contained in a storage medium associated with the information processing system, or may be transmitted to the system via some communication link. For example, such flags could be used to provide synchronization of various kinds, to define the limits of variable length data messages, and to indicate the limits of storage fields assigned to various users in a multiprogramming system.
The typical straightforward approach to filling such a need is to allocate a particular combination of data bits to represent the desired flag. The disadvantage of this approach is that the number of bit combinations which can represent valid data are reduced if some of those combinations must be utilized to represent control flags.
Another approach to the problem is exemplified by U.S. Pat. No. 3,913,068 which describes a system in which data employed for synchronization purposes is arranged in a different code than data which represents information. With the instant invention, special symbols (flags) are coded in the same form as other data thereby conserving code utilization and bandwidth, as well as simplifying the system.
Other prior art of particular interest includes U.S. Pat. No. 3,836,957 and two articles appearing in the IBM Technical Disclosure Bulletin, Vol. 20, No. 9, Feb. 1978, pages 3579-3580 and 3585-3586. These items of prior art are of interest because they deal with responses by a system to syndromes which indicate the presence of a data error. However, they do not suggest utilizing error syndromes for purposes other than error handling. One manner in which the instant invention distinguishes significantly over such prior art is in utilization of predetermined data configurations and error syndromes for special system control.